Hillary Clinton's supporters at the high school in Des Moines offered cookies. They handed out crisps. They even provided the chairman of the caucus, who is nominally independent, with his megaphone - conveniently labelled: "Hillary, Holler for Change."

But this was Barack Obama's night. The old-style organisation, the treats and pleas did not stand a chance against this new wave of caucus-goers who crowded into the cafeteria at the Valley high school in the western suburbs of the city.

The significance of Obama's victory was not that he was the first African-American to win the overwhelmingly white heartland state of Iowa or that he disrupted Clinton's seemingly inevitable march to the White House.

It was that he brought several different kinds of voters - a process that for years has been dominated by hardcore Democrats, and middle-aged and elderly voters - and has seen miserly turnouts even for a sparsely populated state.

The newcomers were both young and middle-aged. Many of the latter were women who had never attended a caucus - a group that should have been owned by Clinton. Sandra Wheat, 66, a first-timer, said that in earlier years: "I had other things to do. I was just not interested." Obama, she said, was an eye-opener - and he had her vote.

Obama's ability to reach out beyond the Democratic base will help sway many who vote in the next contest in New Hampshire. Democrats, desperate after two terms of George Bush, want the candidate with the broadest appeal as their candidate in November's presidential election, and they may judge on Tuesday that Obama is the one.

The catastrophe for Clinton was not just that she lost out to Obama but was forced into a humiliating - albeit by a narrow margin - third place behind John Edwards.

The undoing of her machine was palpable across Iowa well before caucus night with the near rapturous reception Obama enjoyed on the campaign trail. At Clinton events the applause was more dutiful. Voters trickled out of her events impressed by her intelligence, but uninspired.

And on caucus night - despite the predictions that relying on first-time voters was risky - Iowans showed they cared more about inspiration than efficiency.

At one site, set up above a church sanctuary in central Des Moines, old timers said it was the biggest turnout they had ever seen. "This is a crazy amount," said Bob Williams, a retired businessman in his late sixties. "I've never seen it like this."

Many had never voted for a Democrat before. At the check-in tables, workers filled in sheet after sheet of newly registered Democrats. "A lot of people who used to be Republicans and independents are registering Democrats so they can vote for Obama," said Charlie Wittmack, a lawyer.

Amid the crush, the outcome was clear before the first hands were raised in the air in favour of the various candidates. Clinton was outnumbered four to one. At this caucus, she got scarcely more support than Joe Biden who dropped out of the presidential race on Thursday night because of lack of support.

"I think Obama has got a lot of momentum. The message of change is resonating," said a wistful Clinton supporter Julie McElroy, a lawyer who is now a stay-at-home mother of two. Her candidate wasn't out yet though. "She is going to regroup and fight. I would be amazed if she cut tail and ran. It is not in her nature."

But Clinton has only four days left to turn events round, or she could wind up a victim of the new-look politics that has seen the previously leisurely and lengthy caucus and primary election process crammed into a short, explosive month.

She openly acknowledged that yesterday in an email to supporters. "We've got more work to do. That was my first reaction as I saw last night's election results come in. And today in New Hampshire, I'm pounding the pavement looking for every last vote in next Tuesday's primary."

On the late-night plane from Iowa to New Hampshire, her chief strategist, Mark Penn, told reporters she would be sticking to the campaign message she repeated for months in Iowa, even though it proved to be unsuccessful: that she is experienced and Obama is not.

"This is an election that is really going to be about the choice that people have between an experienced leader for change versus leadership with less experience that talks about change," Penn said.

Although she has enjoyed a strong lead over Obama in nationwide polls, suggesting she could do well in California, New York and other big states next month, that could erode if Obama gains momentum. After New Hampshire, the next big contest is South Carolina, and Obama has built an impressive network of support there. She needs to stop him in New Hampshire.

For much of last year, Obama was trailing Clinton in the polls. While his campaign speech won nearly universal acclaim, he was criticised by pundits for failing to show that he had the capacity to fight a tough election.

But Clinton's presumption of inevitability was shaken in late October when she made her first mistake of the primary season in a Democratic debate where she equivocated on a question about immigration. Only days later, Obama delivered an electrifying speech at one of Iowa's main Democratic party events, the Jefferson Jackson dinner.

Obama got another chance to win over Iowa's voters with Oprah Winfrey, who held two events in the state, attracting crowds in the thousands and ensuring that the candidate got a second look.

That made Obama a strong contender, and eventually the victor in Iowa. On the ground in Iowa, Clinton's evasion on the immigration issue in the debate and an ill-conceived ploy to have a campaign worker pose a fake question made her seem exactly the kind of Washington politician of which voters in Iowa are heartily tired.

Many caucus voters admitted that Obama, Clinton or Edwards would all make good presidents. And some in the church that night admitted they made a split-second choice, like Nicole Tuel, 24, who works in marketing.

That moment of decision led Tuel to Obama. "I just thought about it and spoke to a lot of people here that I knew and Oprah was a big draw for me," she said. "I think he will be a great leader, get some new blood into the White House, and get some change for our country."